Summary of Cirrhosis
Transcript for Cirrhosis
When cells are injured or damaged and die off, usually that dead tissue that was previously full of living cells becomes fibrotic, meaning it becomes thickened with heaps and heaps of protein and forms scar tissue.
So when your liver is constantly forced to process alcohol like in alcoholic liver disease, or subject to a viral attack for a long time like in HBV, or anything else that causes a long-term or chronic state of liver cell or hepatocyte destruction and inflammation, your liver can become seriously scarred and damaged to the point where it’s no longer reversible, at which point it becomes fibrotic and in the liver we call this process cirrhosis.
Because it’s usually irreversible, cirrhosis is often referred to as “end-stage” or “late-stage” liver damage.
When liver cells are injured, they start to come together and form what are called regenerative nodules. You can think of these as colonies of living liver cells. These are one of the classic signs of cirrhosis and are why a cirrhotic liver is more bumpy as opposed to a smooth, healthy liver.
Also with cirrhotic liver tissue, you’ll see that in between these clumps of cells or nodules, is fibrotic tissue and collagen.
Here’s a classic histology image of cirrhotic tissue, this clump of cells in the middle is the regenerative nodule, and these blue stains surrounding it are the bands of protein from the process of fibrosis.
If we zoom out a bit and look at it with the naked eye, we’ll again see these nodules, which have fibrotic protein bands in between.
How do these bands of fibrotic tissue form though? Well fibrosis is a process mediated by special cells called stellate cells, that sit between the sinusoid and hepatocyte, known as the perisinusoidal space.
Here’s a pretty basic layout of the basic functional unit of the liver, you’ve got the portal vein and hepatic artery that combine into a sinusoid, which then goes into the central vein, and these are all lined with hepatocytes.
Along with these though you’ve also got a bile duct, and all three constitute a portal triad.
So the perisinusoidal space, which literally means “around the sinusoidal space”, and stellate cells are about here. And usually in healthy tissue, these guys’ main function is to store vitamin A and are otherwise considered quiescent, or sort of dormant.
When the hepatocytes are injured though, they secrete paracrine factors that “activates” and changes the stellate cells.
When activated, the stellate cells lose vitamin A, proliferate, and start secreting transforming growth factor beta1, or TGF-beta, which then causes them to produce collagen, which is the main ingredient in extracellular matrix, fibrosis, and scar tissue.
As this fibrotic tissue builds up, it starts to compress the central veins and sinusoids.
It’s thought that in a healthy, normal state, these cells play key roles in the natural wound-healing process, but when the liver cells are constantly injured, the stellate cells are constantly activated and so they constantly produce collagen and factors that lead to fibrosis.
And this is when complications due to cirrhosis start to crop up.
As the central veins and sinusoids become compressed and push on the fluid inside, their pressure starts to build up, leading to intrasinusoidal (or portal) hypertension, which is this higher pressure in the portal veins.
Higher portal vein pressure means that fluid in blood vessels is more likely to get pushed into tissues and across tissues into large open spaces like the peritoneal cavity.
That’s why cirrhosis leads to excess peritoneal fluid, a condition called ascites, and can result in other complications like congestive splenomegaly and hypersplenism, where the spleen becomes enlarged because all this fluid and blood can’t get into the liver, and backs up into the spleen.
In the same way, your circulatory system starts diverting blood away from the liver because of the high liver pressures, this is known as a portosystemic shunt.
Blood flow follows the path of least resistance and shunts away from the portal system and towards the systemic system of circulation.
Though not fully understood, these changes in portal flow ultimately trigger renal vasoconstriction, so increased resistance in the renal circulation, which decreases blood flow through the kidneys, leading to decreased filtration hepatorenal failure, where kidney failure follows liver failure.